target/i386/tcg: fix a few instructions that do not support VEX.L=1

Match the contents of table 2-17 ("#UD Exception and VEX.L Field Encoding")
in the SDM, for instruction in exception class 5.  They were incorrectly
accepting 256-bit versions that do not exist.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>